I don't mind a 'grey' ending. But is that really what we got? The blue one is pretty positive, Shephard becomes the reapers to defent the weak etc, green the whole galaxy is at peace etc, red is the only grey one really.
I would have preferred the original ending with the dark energy, where the choice was to either destroy the reapers and put your faith in the races of the galaxy, or sacrifice humanity for the greater good to help the reapers solve the dark energy problem.